A material obtained by coating a resin composition containing a near-infrared ray-absorption coloring matter on a transparent substrate to absorb and thereby shield light in the near-infrared region is known as a near-infrared ray-shielding material assured of a high visible light transmittance and a high near-infrared ray-shielding property in the near-infrared region.
As for the near-infrared ray-absorption coloring matter, various combinations of a diimmonium-based compound, an aminium-based compound, a phthalocyanine-based compound, an organic metal complex-based compound and the like have been proposed.
With respect to the resin material used for forming the paint film, use of various thermoplastic resins such as polyester-based resin, acrylic resin, polyurethane-based resin, polyolefin-based resin and polycarbonate-based resin is known.
However, when the above-described near-infrared ray-absorption coloring matter is used alone for obtaining a high near-infrared ray-shielding property in the region of 850 to 1,000 nm, the transmittance in the visible region decreases. Therefore, at least two coloring matters must be mixed and used. Furthermore, for achieving both a high visible light transmittance and a high near-infrared ray-shielding property in the region of 850 to 1,000 nm, out of those near-infrared ray-absorption coloring matters, it is essential to contain at least a diimmonium-based compound represented by formula (5) having small absorption in the visible region and a large absorption coefficient in the near-infrared region.
The diimmonium-based compound conventionally used for the near-infrared ray-shielding resin composition is, for example, a compound represented by the following formula (5) disclosed in Japanese Examined Patent Publication (Kokoku) No. 43-25335 (Patent Document 1), wherein R represents, for example, an alkyl group such as methyl group, ethyl group, propyl group and butyl group, an aryl group or a hydroxy group, and X represents, for example, a perchlorate ion, a fluoroborate ion, a hexafluoroarsenate ion or a hexafluoroantimonate ion. Specific examples of the compound represented by formula (5) which has been heretofore used include a salt of N,N,N′,N′-tetrakis(p-diethylbutylaminophenyl)-p-phenylenediamine-bis(immonium).

Among these salts, in producing a near-infrared ray-shielding laminate, a hexafluoroantimonate of N,N,N′,N′-tetrakis(p-diethylbutylaminophenyl)-p-phenylenediamine-bis(immonium), which exhibits relatively stable weather resistance, has been suitably used.
Such a diimmonium compound has strong absorptivity with a molar extinction coefficient of about 100,000 in the near-infrared region at a wavelength of 850 to 1,100 nm and slight absorption in the visible region at a wavelength of 400 to 500 nm and therefore, provides a yellow-brown transmitted color but, by virtue of its excellent visible light transparency as compared with other near-infrared ray-absorption coloring matters, this compound is an essential component for the near-infrared ray-shielding composition of this embodiment where a high transmittance in the visible region is to be obtained.
However, when the near-infrared ray-shielding layer obtained by mixing such a diimmonium compound and a resin material and coating the resulting resin composition on a transparent substrate is left standing for a long time in a high-temperature high-humidity atmosphere, particularly in a severe environment such as 80° C.-relative humidity 95% atmosphere simulating marine transportation of the product, the diimmonium compound inevitably undergoes alteration, in view of composition, to cause a problem that the variation of chromaticity x and y increases. Thus, improvement of durability is demanded.
As for the paint film exhibiting relatively stable durability when left standing in a high-temperature high-humidity condition for a long time, a near-infrared ray-shielding material obtained by coating a resin composition using a polyester-based or polycarbonate-based resin having a high glass transition point on a transparent substrate is known but, generally, such a resin material having a high glass transition point is sparingly soluble in a solvent and at the time of preparing the resin composition, a solvent having high toxicity and allowing for very rapid drying, such as dichloromethane and chloroform, needs to be used, giving rise to a problem in the stability as the resin composition, for example, film formation is difficult due to easy occurrence of brushing during coating or because the paint itself is readily gelled. Furthermore, despite good long-term stability in a high-temperature high-humidity condition, there is a problem that the variation of chromaticity x and y, between before and after a xenon accelerated weather resistance test for 48 hours, becomes significantly large.
Patent Document 1: Kokoku No. 43-25335, page 13